2-Furaldehyde is a useful compound which can be used as a raw material for producing furan, tetrahydrofuran, a furan resin, etc. 2-Furaldehyde is generally not produced from a raw material derived from petroleum, but is produced using a sugar derived from a plant as a raw material. Therefore, 2-furaldehyde is not classified into a chemical product derived from a petroleum raw material but is classified into a chemical product derived from a plant raw material.
As a method for producing 2-furaldehyde, a method in which a raw material containing a five-carbon sugar such as a pentosan or a pentose is reacted in the presence of an acid catalyst to dehydrate the five-carbon sugar, whereby 2-furaldehyde is obtained has been conventionally known (NPL 1 and NPL 2). Such a five-carbon sugar is contained in hemicellulose, etc. contained in an agricultural waste material such as a sugar cane residue (bagasse) resulted from extraction of juice, corncobs, or wood.
However, the above-described agricultural waste material serving as a representative raw material containing such a five-carbon sugar has a limit to the accumulation of the raw material. Further, the content of hemicellulose in the above-described representative raw material is not so high. For example, the content of hemicellulose in wood is at most about 25%. Due to this, a method for obtaining 2-furaldehyde from a five-carbon sugar has a problem that the yield of 2-furaldehyde per raw material to be used is low. In view of this, there has been a demand for a method for obtaining 2-furaldehyde from a constituent component which exits in a plant more abundantly.
Therefore, attention is paid to cellulose which is a main component of wood and exists abundantly in nature as a natural fiber. Cellulose is a linear polymer containing glucose which is a six-carbon sugar, as a main component. However, since cellulose has high crystallinity, it is difficult to hydrolyze cellulose into a six-carbon sugar serving as a constituent component. Further, it is known that when a six-carbon sugar obtained by hydrolyzing cellulose is reacted in the presence of an acid catalyst to effect dehydration in the same manner as the above-described method for obtaining 2-furaldehyde from a five-carbon sugar, the six-carbon sugar is not inverted into 2-furaldehyde, but inverted into 5-hydroxymethyl-2-furaldehyde (for example, PTL 1 and NPL 3).
On the other hand, a method for producing 2-furaldehyde from a raw material containing a six-carbon sugar is also proposed. Cellulose which is a main component of wood contains glucose which is a six-carbon sugar (a hexose) as a constituent unit. PTL 2 and NPL 4 propose a method for obtaining 2-furaldehyde by heating cellulose in an aprotic polar solvent in the presence of sulfuric acid.